Lightly season prawns with salt and pepper. Add cornflour and toss well together to combine. Set aside.
Place wok over medium low heat and pour in oil. Add in raw cashew nut and slowly heat the oil ( cashewnuts will be fried at the same time the oil is being heated up) Fry cashewnuts till it turns lightly golden and dish out before it begins to turn dark brown. Drain from oil and set aside.
heat the same oil in the wok until hot and deep fry the prawns for 2-3 minutes. Remove and set aside.
Put 2 tbsp oil in a clean wok and fry ginger and garlic until fragrant.Add onions and dried chillies. Fry for a minute. Pour in the sauce ingredients and bring to a boil.
Add in the prefried prawns to the wok.Mix briskly. Thicken sauce with the cornflour mixture and toss in the cashewnuts. Dish out and serve hot with rice.